.gamma.-Poly(glutamic acid) (hereinafter ".gamma.-PGA") is a polymer which is biodegradable. However, the utility of .gamma.-PGA has been limited. For example, synthetic methods typically result in a .gamma.-PGA polymer, or corresponding side chain ester derivatives, having a molecular weight of less than about 10,000, which significantly limits the utility, such as theological or mechanical utility, of the polymer. See, Kovacs et al., Canad. J. Chem., 47: 3670 (1969); Hardy et al., J. Chem. Soc., 6: 605 (1972); Honda et al., Macromol. Chem., 176: 1643 (1978). Also, .gamma.-PGA is typically water-soluble, which limits the utility of this material in both environmental and medical applications.
One attempt to increase the molecular weight of .gamma.-PGA has been to ferment a bacteria, Bacillus licheniformis, which releases a naturally-produced .gamma.-PGA into the fermentation broth. However, naturally-produced .gamma.-PGA degrades over time, thereby significantly diminishing the molecular weight of naturally-produced .gamma.-PGA which can be recovered.
Therefore, a need exists for a method of forming .gamma.-PGA and derivatives thereof which overcome the aforementioned problems.